The area of application of the subject high pressure relief valve is preferably that of relieving the pressure on the hot-separator product of the hydrogenative liquefaction of coal. This product contains solid components in the form of ash, catalyst, and unreacted coal components. The pressure relief valve is provided to lower the pressure from up to 700 bar to a lower, intermediate level or to normal pressure. Such hot-separator residues are produced at temperatures between about 380.degree. and 480.degree. C., and the required depressurization from operating pressure to the lower pressure results in the residue's causing substantial abrasive wear and/or appreciable corrosion of parts of the high pressure relief valve exposed to them. Such wear and/or corrosion is due to the high flow speeds which develop, to the changes of flow direction which occur in the high pressure relief valve, and to the abrasive characteristics of the solid components of the hot-separator residues. The affected valve parts are particularly the valve poppet, the valve seat, the valve stem, miscellaneous housing parts of the valve, and the seat bore of the valve seat with the adjoining pipe running into the pressure relief container.
As a rule, the valve seat inserts are comprised of abrasive-resistant hard materials, and they may be provided as replaceable parts.
It has been found that exponentially high wear occurs in connection with degasification and evaporation of the hot-separator residue depressurized from operating pressure to the relief pressure, due to substantial acceleration of solid particles as well as liquid particles, in the presence of hydrogen. Because of the presence of hydrogen, the flow directions of such particles may be up to 180.degree. against the general flow direction.
A pressure relief valve for slurries, e.g., is the subject of Eur. OS No. 0 085 251.